Altaic etymology :

Comments:Martin 248. In Kor. the word seems to be related to kằr- 'to grind, pulverize' - but this meaning is probably secondary (the verb originally means 'to polish, whet'). The tone discrepancy between Kor. and Jpn. should be explained either by the secondary influence of this verbal stem in Korean, or by contraction in Japanese (where *kuà < *gur(e)-ga); the first explanation seems more probable because the vowel reflex in Korean is also not quite regular (*-o- would be normally expected).